Former swimming pools have included a row of spaced braces fastened to the outer side of each of the walls as shown in U.S. Pat. No. 3,511,002 issued to G. C. Fox on May 12, 1970. For a swimming-pool having a cover, the cover and a wind-up drum are housed in a receptacle that is installed on a support or foundation that is independent of that for an adjacent end wall. Since the cover must be extended at a particular level with respect to the heights of the walls of the pool, tedious effort is required for installation of a support for positioning the receptacle or housing level precisely at the required height.